Can proton mass be measured without assuming inertia?

[bubsir]

Direct gravitational measurements of subatomic particles seems impossible. Has it been done/tried? The mass of the proton as I know it is always "indirectly" determined by (for example) bending a beam of charged protons in a magnetic field.

 

[Vanadium 50]

It's been done with neutrons.

But what's wrong with using a box of hydrogen?

 

[sophiecentaur]

Could that be because you can gather a large number of neutrons together without them scattering in all directions before you can measure them?
Hydrogen - yes, why not? Or any other atom, for that matter.